Abstract: An electrolyte of an energy storage device includes a non-aqueous solvent, an electrolyte salt including LiPF6, and at least two compounds selected from among a phosphite ester compound represented by a formula 1, a compound configured to form lithium and a complex and including a formation constant equal to or greater than 102, difluorophosphate represented by a formula 2, and a phosphate ester compound represented by a formula 3, the at least two compounds including at least the phosphite ester compound represented by the formula 1: where each of R11, R12, and R13 is independently one of a monovalent hydrocarbon group and a monovalent fluorinated hydrocarbon group, where M21+ is one of lithium ion (Li+) and sodium ion (Na+), where each of R31, R32, and R33 is independently one of a monovalent hydrocarbon group and a monovalent fluorinated hydrocarbon group.

Abstract: A process for controlling operation of a nuclear reactor in which first control means is operated to cause reactor power to rise to a level at which a pellet-clad-mechanical-interaction begins to take place between a cladding and pellets of a fuel element. After interrupting the operation of the first control means, second control means is operated to cause the reactor power to rise to a preset level, the second control means being capable of effecting finer control of the reactor power than the first control means. When the reactor power deviates from the preset level with the progress of the reactor operation in the preset level, the second control means is operated so as to maintain the reactor power at the preset level.